The reason is this. During the afternoon, the sun's heating is the strongest and this heating destabilizes the atmosphere. The sun heats the earth's surface, so the atmosphere is really heated from the bottom upwards. So, the air at the lowest level of the atmosphere is heated first. The warm air rises since warm air is lighter and less dense than the cooler air aloft. This mixing of the air helps to bring down stronger winds blowing at higher levels in the atmosphere. These stronger winds are blowing during the morning hours above the surface, but the air is many times too stable to allow the fast moving air to get to the surface. During the morning hours, an ģinversionī is usually present which means that the lowest level of the atmosphere is cooler than the air aloft. This stable layer of cool air literally prevents the winds higher up in the atmosphere from mixing down to the surface. As soon as the sun heats the ground, this inversion begins to break down and the winds mix down to the surface. However, there are some exceptions. During stormy periods, the mornings can be just as windy as the afternoons. Also, if a strong cold front moves through your area in the early morning hours, the winds may be stronger immediately following the frontal passage and then die down in the afternoon or evening.